The present invention concerns a reforming catalyst and a catalytic reforming process using the catalyst.
When petroleum hydrocarbon fractions in the gasoline boiling range are mixed with hydrogen and passed over a reforming catalyst such as a platinum-rhenium-alumina catalyst at conventional reforming conditions, the value of such hydrocarbons for use as fuel in automobile engines is improved.
One of the problems encountered in commercial reforming operations is fouling or coking of the catalyst. In order to maintain a steady rate of conversion in reforming, the temperature of operation must be increased more-or-less continuously as the fouling of the catalyst becomes progressively worse. Eventually, the reforming operation must be discontinued to replace or regenerate the catalyst. Shutting down such a refinery operation periodically is costly and tedious. It is, therefore, highly desirable to lower the fouling rate of a reforming catalyst to prolong its useful life.
Platinum-rhenium-alumina reforming catalysts are normally prepared by impregnating previously calcined alumina with a platinum compound and a rhenium compound. For example, a platinum-rhenium-alumina reforming catalyst may be prepared by commingling the alumina support with aqueous solutions of chloroplatinic acid and perrhenic acid. After the aqueous solutions of the metals are contacted with the alumina, the alumina is dried to remove the water, leaving the metal compounds deposited on the alumina. The alumina is then subjected to relatively low-temperature drying and subsequently is calcined or oxidized.
The halogen component has been added to catalysts in various ways, e.g., by addition of halogen in halogen compounds of metals during the metals-impregnation step. Total halogen content in reforming catalysts has been described in the range from 0.1 to 3.5 weight percent of the final catalyst. Calcination temperatures utilized to provide suitable alumina bases for catalysts have been taught between 850.degree. F and 1300.degree. F.
It has been taught in the art to add salts or acids to a chloroplatinic acid impregnating solution used with an alumina base or carrier, in order to distribute platinum on the carrier in a more efficient manner. The art teaches that a competitor adsorbate such as hydrochloric acid will effect a uniform distribution of platinum onto alumina. Competitor adsorbates which have been taught as useful in this regard include aluminum trinitrate, sodium nitrate, aluminum chloride and ammonium nitrate. Competitor adsorbates which have been taught as harmful in this same regard include nitric acid, hydrochloric acid, ammonium chloride and sulfuric acid. Such teaching as to competitor adsorbates may be found in "Industrial & Engineering Chemistry", Vol. 51, No. 8, and Vol. 49, No. 2.